The morphology of the beach backshore and foreshore at Huiquan Bay,Qingdao,China,is characterized by a single intertidal sandbar system with a spring tide range of 4.59 m.The beach was measured with a laser total station of Leica TPS402.Contours of the beach were generated using data collected in March and November 2005.The survey method provided 2 mm measuring accuracy and 4-10 m horizontal spacing.The net accretion volume of the foreshore was about 11,215 m3 from March to November.After sand sculpture activity,the axis of the sand trough migrated onshore from about 3.5 m to 17.5 m on the foreshore beach in November.At the same time,the axis of the sandbar crest migrated onshore no more than 42.25 m on the northwest foreshore;and it migrated offshore no more than 23.75 m on the southeast foreshore.On the northwest and southeast foreshore beach,two strips of erosion areas with a thickness of 0-0.2 m appeared on the sandbar crest.Accretion occurred at the bottom of the sand trough with a thickness of ～0.2-0.6 m.The sandbar height decreased after sand sculpture activity,and it was no more than 0.7 m in March and 0.6 m in November.Human activities,such as sand digging on the sandbar crest during sand sculpture activity,also can disturb the beach morphology of intertidal bar systems.This phenomenon also was validated by comparison of beach morphology,the results of a color artificial tracer experiment and a sediment transportation trend prediction.
The evolution and variation history of the Tsushima warm current during the late Quaternary was reconstructed based on the quantitative census data of planktonic foraminiferal fauna, together with oxygen and carbon isotope records of mixed layer dweller G. ruber and thermocline dweller N. dutertrei in piston core CSH1 and core DGKS9603 collected separately from the Tsushima warm current and the Kuroshio dominated area. The result showed that the Tsushima warm current vanished in the lowstand period during 40―24 cal ka BP, while the Kuroshio still flowed across the Okinawa Trough, arousing strong upwelling in the northern Trough. Meanwhile, the influence of freshwater greatly increased in the northern Okinawa Trough, as the broad East China Sea continental shelf emerged. The freshwater reached its maximum during the last glacial maximum (LGM), when the upwelling obviously weakened for the lowest sea-level and the depression of the Kuroshio. The modern Tsushima warm current began its development since 16 cal ka BP, and the impact of the Kuroshio increased in the middle and north- ern Okinawa Trough synchronously during the deglaciation and gradually evolved as the main water source of the Tsushima current. The modern Tsushima current finally formed at about 8.5 cal ka BP, since then the circulation structure has been relatively stable. The water of the modern Tsushima cur- rent primarily came from the Kuroshio axis. A short-term wiggle of the current occurred at about 3 cal ka BP, probably for the influences from the enhancement of the winter monsoon and the depression of the Kuroshio. The cold water masses greatly strengthened during the wiggle.
LI TieGangSUN RongTaoZHANG DeYuLIU ZhenXiaLI QingJIANG Bo
To reconstruct the formation and evolution process of the warm current system within the East China Sea (ECS) and the Yellow Sea (YS) since the last deglaciation, the paleoceangraphic records in core DGKS9603, core CSH1 and core YSDP102, which were retrieved from the mainstream of the Kuroshio Current (KC), the edge of the modern Tsushima Warm Current (TWC) and muddy region under cold waters accreted with the Yellow Sea Warm Current (YSWC) respectively, were synthetically analyzed. The results indicate that the formation and evolution of the modern warm current system in the ECS and the YS has been accompanied by the development of the KC and impulse rising of the sea level since the last deglaciation. The influence of the KC on the Okinawa Trough had enhanced since 16 cal kyr BP, and synchronously the modern TWC began to develop with the rising of sea level and finally formed at about 8.5 cal kyr BP. The KC had experienced two weakening process during the Heinrich event 1 and the Younger Drays event from 16 to 8.5 cal kyr BP. The period of 7-6 cal kyr BP was the strongest stage of the KC and the TWC since the last deglaciation. The YSWC has appeared at about 6.4 cal kyr BP. Thus, the warm current system of the ECS and the YS has ultimately formed. The weakness of the KC, indicated by the occurrence of Pulleniatina minimum event (PME) during the period from 5.3 to 2.8 cal kyr BP, caused the main stream of the TWC to shift eastward to the Pacific Ocean around about 3 cal kyr BP. The process resulted in the intruding of continent shelf cold water mass with rich nutrients. Synchronously, the strength of the YSWC was relatively weak and the related cold water body was active at the early-mid stage of its appearance against the PME background, which resulted in the quick formation of muddy deposit system in the southeastern YS. The strength of the warm current system in the ECS and the YS has enhanced evidently, and approached to the modern condition gradually since 3 cal kyr BP.
